Flu could make you 40 per cent more likely to have a stroke – and the risk can last for up to a year, a study has found.
Researchers aren’t sure why the link exists, but said it could be due to inflammation – internal swelling – caused by the flu.
The finding adds to previous research which has suggested the flu vaccine can reduce your risk of a stroke.
Flu vaccination rates have dwindled in recent years, with fewer than half of vulnerable people having the jab this winter.
Influenza is already known to be able to lead to serious and potentially life-threatening complications such as pneumonia, sepsis and heart disease.
Flu could make you 40 per cent more likely to have a stroke – and the risk can last for up to a year, a study led by Columbia University in New York has found
The scientists, led by Dr Amelia Boehme, from Columbia University in New York City, looked at the medical records of 30,912 people who had been admitted to hospital after suffering a stroke.
Study participants were 49 per cent male, 20 per cent black, 84 per cent from urban areas, and had an average age of 72 years old.
Researchers looked at each patient’s hospitalisation history for the two years leading up to their stroke.
They found people had a 40 per cent higher chance of having a stroke if they had been admitted to hospital with flu-like symptoms within the past 15 days.
The risk remained for a year, the findings, to be presented in Honolulu at the American Stroke Association’s International Stroke Conference 2019, showed.
Professor Philip B Gorelick, an American Heart Association volunteer and professor at Michigan State University College of Human Medicine, said: ‘The association occurred within 15 days. That’s important for people to know because if they get the flu, they wanna be on the lookout for symptoms of stroke, especially early on after the flu.’
The participants’ data was analysed after accounting for urban or rural status, sex and race. But the link didn’t seem to change between groups.
Dr Boehme said: ‘We were expecting to see differences in the flu-stroke association between rural and urban areas.
‘Instead we found the association between flu-like illness and stroke was similar between people living in rural and urban areas, as well as for men and women, and among racial groups.’
There are various possible reasons behind the flu-stroke link, but no definitive conclusion has been reached.
Researchers suspect it could be due to inflammation caused by the flu infection.
Another study, by the same researchers, found an increased risk of a neck artery tear after having the flu.
Neck artery tears, formally called a cervical artery dissection, is when one of the large blood vessels in the neck is damaged, causing blood clots to develop.
It is a leading cause of stroke because it affects the blood supply to the brain.
The study, which will be presented at the same conference, reviewed 3,861 cases of neck artery tears in the New York State Department of Health figures for 2006 to 2014.
They found 1,736 instances of flu-like illness and 113 of influenza during the three years preceding cervical artery dissection.
Patients were more likely to have suffered a flu-like illness in the 30 days before their artery tear than they were at the same time in previous years.
Madeleine Hunter, the study’s lead author and a second-year medical student at Vagelos College of Physicians and Surgeons at Columbia University in New York City, said: ‘Our results suggest that the risk of dissection fades over time after the flu. This trend indicates that flu-like illnesses may indeed trigger dissection.’
Professor Gorelick said: ‘Cervical or neck dissections make up about two per cent of all strokes and up to 25 per cent of strokes in persons who are under 45 years of age. So this is specifically important to people who are in that under 45 age group, but not exclusively.’
The NHS encourages pregnant people and anyone over the age of 65 to have an annual flu jab.
Recent figures show that only 44.8 per cent of pregnant women and 71.2 per cent over 65 year-olds have been vaccinated this season.
This is compared to 47.1 per cent of pregnant women and 72.4 per cent of over 65 year-olds last year.
Both the Center for Disease Prevention and Control in the US and the NHS in the UK also recommend heart failure patients get the flu jab.
Viral infections, such as flu, can put added stress on the body and raise blood pressure, which can cause heart attacks or stroke in vulnerable people.